This application claims benefit of Japanese Patent Application No. 11-348264 filed on Dec. 8, 1999, the contents of which are incorporated by the reference.
The present invention relates to reception power level calculating circuits and receivers using the same and, more particularly, to reception power level calculating circuits and receivers using the same, which can be suitably used for CDMA communication system mobile stations.
FIG. 3 schematically shows the construction of a receiver having an AGC (Automatic Gain Control) function. Referring to the Figure, received signal is fed from an antenna 1 to a front terminal circuit 2. The front terminal circuit 2 comprises a duplexer, an amplifier, a band-pass filter, a down-converter, etc., and serves to remove the received signal components outside a desired frequency band and also amplify and frequency convert the received signal. The output of the front terminal circuit 2 is fed to an AGC amplifier 3. The AGC amplifier 3 controls the gain for the received signal on the basis of a control voltage corresponding to the reception power level, and feeds out its output to a demodulating circuit 4. The demodulating circuit 4 demodulates the received signal, and feeds out the demodulated signal to an A/D (analog-to-digital) converter 5. The A/D converter 5 digitally converts the analog demodulated signal, and feeds out the digital demodulated signal to a channel filter 6.
The channel filter 6 attenuates the frequency components outside the desired frequency band in the neighborhood of a desired frequency, and feeds out the attenuated signal to a succeeding base-band circuit 7. The base-band circuit 7 executes a base-band processing on the received signal, and also calculates the ratio (SIR: Signal to Interference Ratio) of the power level of desired wave in the received signal to interference frequency power level. A power level calculating circuit 10 calculates the power level of received signal from the output of the A/D converter 5, and feeds out the difference of the received signal power level from a preset reference power level. This difference corresponds to the difference between the actual level of power fed to the A/D converter 5 and a reference power level to be received. An integrating circuit 9 integrates the power level difference.
The integrating circuit 9 feeds out gain control data thus obtained for controlling the gain of the ACG amplifier 3 corresponding to the antenna terminal reception power level. A D/A converter 8 converts the gain control data to an analog control voltage for controlling the gain of the amplifier 3. It is adapted that the integrating circuit 9 reports or supplies the obtained integration data as antenna terminal reception power level to the band-pass circuit 7.
In CDMA communication system which is used for mobile communication, spread codes such as PN (Pseudo Random Noise) codes are used for the spread spectrum of communication signal, and the communication signal is recognized on the basis of such spread codes. The CDMA system features that simultaneous communication among a plurality of radio terminals or via a plurality of channels is possible at the same frequency. The CDMA system also features that the received signal can not be demodulated unless the signal is multiplied by the same spread code as spread code used on the transmitting side at the same timing as thereon, and that the received signals with different spread codes or different spread timings, i.e., communication signals from other radio units or other channel signals, are all introduced as noise into the received signal band.
A case will now be considered, in which a plurality of CDMA system mobile stations, found near and remote from the base station of mobile communication, are in communication therewith. When the mobile stations near and remote from the base station are in communication therewith at the same frequency and the same transmission power level, a problem arises, from a view of the base station receiving terminal, that the transmission power levels of the communicating mobile stations near the base station are higher than the transmission power levels of remote communicating mobile stations so that the signals transmitted from the remote mobile stations are just like buried in the signals transmitted from the near mobile stations. This problem is known as near-remote problem. In view of the above features of the CDMA system, the base station cannot correctly demodulate the transmitted signals from the remote mobile stations because of the fact that the transmitted signals contain near mobile base station signals introduced in the reception band frequency.
In the CDMA system, such near-remote problem is solved by relatively frequent, stringent and highly accurate transmission power level control. Specifically, the transmission power level control is executed to make the near mobile station transmission power level lower and the remote mobile station transmission power level higher. The same control is executed as for the transmission power level from the base station to the mobile stations. For the transmission power level control, the base-band circuit in the receiver, i.e., mobile station side, should have correct antenna terminal reception power level. Accordingly, as shown in FIG. 3, the output of the integrating circuit 9 in the AGC circuit is reported as the antenna terminal reception power level to the base-band circuit 7.
As described above, the base-band circuit 7 computes the power level of the desired frequency for transmission power level control as well as computing the received signal SIR. The computation of the desired frequency power level requires a calculation given as:
(antenna terminal reception power level)xc3x97(desired wave power level)/(full reception power level). 
The antenna terminal reception power level is the full reception power level. The ratio (desired frequency power level)/(full reception power level) is obtained and known in the base-band circuit 7, and the base-band circuit 7 is thus adapted to compute the required desired frequency power level by using the antenna terminal reception power level corresponding to the AGC circuit output, which power level is reported from the integrating circuit 9.
The prior art technique shown in FIG. 3, however, has a problem that the antenna terminal reception power level reported to the base-band circuit 7 does not actually correspond to the received signal fed thereto. Therefore, the base-band circuit 7 feeds out erroneously calculated power levels of desired frequency and interference frequency as its output, and also it is impossible to obtain right transmission power level control.
The reason for this resides in that the antenna terminal reception power level reported to the base-band circuit 7 corresponds to the received signal input to the A/D converter 5 while the received signal input to the base-band circuit 7 has been reduced in power level by the power level attenuation outside the desired frequency band in the passing of the output of the A/D converter 6 through the channel filter 6. This means that the received signal inputs to the A/D converter 5 and the base-band circuit 7, respectively, are different in power level. This leads to a difference of the corresponding antenna terminal reception power level.
Another prior art technique will now be described with reference to FIG. 4. In FIG. 4, parts like those in FIG. 3 are designated by like reference numerals. In the prior art technique shown in FIG. 4, unlike the prior art technique of FIG. 3, a power level calculating circuit 11 for power level calculation to control the gain of AGC amplifier, is provided not on the input terminal side but on the output terminal side of channel filter 6.
This circuit construction, however, poses a problem of saturation of the A/D converter 5. Saturation of the converter 5 results in power level increase or swelling outside the desired frequency band, thus resulting in deterioration of adjacent channel selectivity characteristic and so forth. This is so because the gain of the AGC amplifier 3 is determined by calculating the power level of received signal having passed through the channel filter 6. As the power passes through the channel filter 6, the power level outside the desired frequency band is attenuated, resulting in power level lower than the power level of the input to the A/D converter 5. The gain of the amplifier 3 is determined on the basis of the power level having been reduced by the passage of power through the channel filter 6, and therefore an increased value of gain is set. However, saturation takes place since signal containing power outside the desired frequency band is fed to the A/D converter 5.
An object of the present invention is to provide a reception power level calculating circuit and a receiver using the same, in which the A/D converter is not saturated and permits report of accurate antenna terminal reception power level to the base-band circuit.
According to an aspect of the present invention, there is provided a reception power level calculating circuit for a receiver comprising an AGC amplifier for amplifying received signal, a demodulating circuit for demodulating the output of the AGC amplifier, an analog-to-digital converter for converting the demodulation output of the demodulating circuit to a digital signal, a filter for attenuating the digital output of the analog-to-digital converter outside a desired frequency band, a base-band circuit for base-band processing the output of the filter, an AGC control reception power level calculating means for calculating a reception power level to generate a control signal for controlling the AGC amplifier, an attenuated power level calculating means for calculating the power level having been attenuated in the filter, and a power level correcting means for correcting the result of calculation in the AGC control reception power level calculating means with the result of calculation in the attenuated power level calculating means and reporting the corrected power level to the base-band circuit.
The AGC control reception power level calculating means includes a means for computing the output power level of the analog-to-digital converter, and a control voltage generating means for generating the control voltage on the basis of the computation output of the computing means. The attenuated power level calculating means includes a means for computing the difference between the output power levels of the filter and the analog-to-digital converter and a means for computing the difference between the computed difference and the computed result by the control reception power level calculating means.
According to another aspect of the present invention, there is provided a receiver comprising an AGC amplifier for amplifying received signal, a demodulating circuit for demodulating the output of the AGC amplifier, an analog-to-digital converter for converting the demodulation output of the demodulating circuit to a digital signal, a filter for attenuating the digital output of the analog-to-digital converter outside a desired frequency band, a base-band circuit for base-band processing the output of the filter, an AGC control reception power level calculating means for calculating a reception power level to generate a control signal for controlling the AGC amplifier, an attenuated power level calculating means for calculating the power level having been attenuated in the filter, and a power level correcting means for correcting the result of calculation in the AGC control reception power level calculating means with the result of calculation in the attenuated power level calculating means and reporting the corrected power level to the base-band circuit.
The AGC control reception power level calculating means includes a means for computing the output power level of the analog-to-digital converter, and a control voltage generating means for generating the control voltage on the basis of the computation output of the computing means. The attenuated power level calculating means includes a means for computing the difference between the output power levels of the filter and the analog-to-digital converter. The base-band circuit receives a report from the power level correcting means and uses the received report as data for power level control with respect to the opposite side of communication. The receiver is used in a CDMA communication system mobile station.
According to other aspect of the present invention, there is provided a receiver in which received signal through an antenna is amplified by AGC amplifier, decoder, A/D converted by A/D converter, suppresses frequency band outside a desired frequency by a channel filter and the filtered output is processed by a base-band circuit, A receiver in which received signal through an antenna is amplified by AGC amplifier, decoded, and A/D converted by A/D converter, frequency band outside a desired frequency is suppressed by a channel filter and the filtered output is processed by a base-band circuit, comprising: power calculator for calculating power signal based on the digital data from the A/D converter; gain controller for determining a difference signal between the power signal and a predetermined reference level determined based on the input range of the A/D converter, integrating the difference signal, and converting the integrated difference signal to an analog signal to supply the converted analog signal to the AGC amplifier as a gain control signal; and subtracter for subtracting an attenuation power level from the integrated difference signal and supplying the subtracted signal to the base-band processor as a reference signal. The attenuation power level of the channel filter is determined by a difference between the input and output of the channel filter. The base-band processor determines SIR, i.e., ratio between the desired frequency power level contained in the received signal and interference power level and controls the transmission power level on the basis of the determined SIR. The receiver as set forth in claim 1 is a receiver in a mobile station in CDMA communication system.
The receiver using the above reception power level calculating circuit according to the present invention, can serve as a CDMA communication system mobile station. The base-band circuit features that it uses a report received from the power correcting means as data for power level control with respect to the opposite side of communication.
In operation and function according to the present invention, the received signal power level is calculated both before and after the passing of power through the channel filter provided as a stage succeeding the A/D converting circuit. It is thus possible to permit accurate antenna terminal reception power level to be reported to the base-band circuit without saturation of the A/D converting circuit.
Specifically, a first power level calculating circuit calculates the power level of received signal, which has been digitally converted in the A/D converting circuit, and thus feeds out the difference of the calculated power level from a reference power level to be received. An integrating circuit integrates the power level difference, and its integration output represents the antenna terminal reception power level and is used for controlling the AGC amplifier. Since the difference between the power level fed to the A/D converting circuit and the reference power level to be received is fed back to the AGC amplifier, the received signal input to the A/D converting circuit does not exceed the input range thereof, and no saturation of the A/D converting circuit takes place.
A second power level calculating circuit for computing the output power level of the channel filter, calculates the power level of received signal after the components outside the desired frequency band have been attenuated in the channel filter. The extent of power level attenuation in the channel filter, can be expressed by the difference of the power level calculated in the second power level calculating circuit from the power level calculated in the first power level calculating circuit. The received signal which is fed to the base-band circuit, has passed through the channel filter and is thus lower in power level than the power level fed to the A/D converter by the extent of attenuation in the channel filter. This means that the antenna terminal reception power level to be reported to the base-band circuit, should be corrected to a level, which represents the difference that is obtained by subtracting the difference between the results of calculation in the two power level calculating circuits from the result of integration in the integrating circuit. By this correction, a coincidence relation of the reception power level fed to the base-band circuit and the antenna terminal reception power level report from each other is obtainable.